The proposed investigation will determine the interrelationship of individual neurons and functionally related groups of neurons at the margins of an experimental epileptogenic focus. The spatial extent of the penicillin-induced epileptogenic cortex is defined in terms of a retinal activation field; this is a circumscribed area whose stimulation by light evokes a characteristic epileptiform wave. Cortex represented by the margins of the activation field will be explored by a microelectrode to determine the degree and character of involvement of individual units in the epileptogenic phenomenon. The units will be defined as to their receptive field orientation specificity, their receptive field location with respect to the activation field and ocular dominance. The data so obtained will determine to what degree physiologically related groups of neurons continue to act as a unit during epileptogenesis. Such data will provide information regarding some mechanisms of the neural aggregate response in epileptogenesis and perhaps indicate an elementary unit of epileptogenesis.